A train speeds past a pole in 15 seconds and a platform 100 m long in 25 seconds. Its length is:

Given Data

• Time to pass a pole = 15 s
• Time to pass a 100 m platform = 25 s
• Required: train length

Step 1: Speed from pole crossing
Let train length = L m. Speed v = L ÷ 15 m/s

Step 2: Use platform crossing
25 = (L + 100) ÷ v = (L + 100) ÷ (L/15)⇒ 25L = 15L + 1500 ⇒ 10L = 1500 ⇒ L = 150 m

Checks & Common Pitfalls

• For a pole, use only train length to get speed.
• For a platform, add train and platform lengths.

Final Answer
The train length is 150 m.